Compress an image to 300 KB
300 KB is preset and reserved for the one image that has to look good; each file gets its own search for the highest JPG or WebP quality that fits under it.
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The CMS style guide says every image under 300 KB. The hero photo for the post, straight from the camera, is 4.2 MB, and the media library either refuses it or accepts it and quietly makes the page slow. Or a performance audit already told you, pointing at pictures that looked fine over your own Wi-Fi.
300 KB is a reasonable ceiling for the one image that has to look good, and a bad default for every image on the page. The arithmetic is plain: on a 1.6 Mbps connection, to take one example, 300 KB takes about 1.5 seconds to arrive, and five of them are 1.5 MB, roughly 7.7 seconds of image download. Spend the 300 KB on the hero and go lighter below it.
The target here is fixed at 307,200 bytes and the format row starts on JPG. The search for the quality that fits runs on your machine, per file, so the photo reaches no server before the media library does. Width is what decides how good 300 KB looks, so give a camera-size hero a Max width (px) before you generate.
How it works
The width belongs to the slot, so decide it before you generate; then check the format and read the cards.
Drop the post images in
Drag the whole set, click Choose images, or paste a screenshot with Ctrl+V on desktop. JPG, PNG, WebP, GIF, BMP, SVG and iPhone HEIC all load; HEIC pulls a decoder of about 1 MB the first time and is decoded on your device.
Check the format, skip the slider
The panel opens on JPG with 300 KB applied and the quality slider ignored, since the search chooses that number; switch the format row to WebP when the site is yours. For a camera-size hero, fill in Max width (px) first: as a starting point we suggest 1,600–2,000 px for a full-width slot or 1,200–1,600 px inside the post.
Generate, compare, download
Press Generate images and read each card against its slot: new size beside old, the percentage cut, the output width and height, and target met, or smallest possible when no quality got the file under 300 KB. Compare lays a slider over the original, useful for checking a hero's sky for banding, and the finished set downloads as one .zip for the media library or one file at a time.
Why 300 KB fits one hero and not the whole page
Take a 1.6 Mbps connection as the example. On it, 300 KB of image is about 1.5 seconds of download, and each additional 300 KB image adds another 1.5 seconds of data. The table is that multiplication; the last column is our suggestion.
| Images at 300 KB | Image weight | Download at 1.6 Mbps | What to do |
|---|---|---|---|
| 1 (hero only) | 300 KB | about 1.5 s | Compress here |
| 3 | 900 KB | about 4.6 s | Hero here, body photos at 200 KB |
| 5 | 1.5 MB | about 7.7 s | Body photos at 100–200 KB, lazy-loaded |
| 10 (gallery) | 3 MB | about 15 s | Thumbnails under 100 KB |
Width decides what 300 KB looks like
The budget is 307,200 bytes, about 2.46 million bits. Over a 12-megapixel camera frame that is 0.2 bits per pixel. Resized to 1,600 px wide, the same frame gets roughly 1.3 bits per pixel, more than six times as much.
A full-size hero dropped straight in is left to the steps: if quality 50 does not fit at full size, the page shrinks the frame 15% at a time and searches again, landing on a width the steps picked rather than the theme. In a test of ours with a 12-megapixel photo in September 2026, that width was 2,456 px. Type the slot's width in Max width (px) and the search runs on the resized image instead. The stages are laid out in how to reduce image file size.
JPG or WebP on a site you control
JPG is the preset of every target page here. On a site you control, switch the format row to WebP: MDN lists support in Chrome, Edge, Firefox, Opera and Safari, and Google's own study put it 25% to 34% smaller than JPEG at the same SSIM index. Under a fixed 300 KB cap that saving comes back as quality: the search can stop higher, or the same quality fits at a larger width.
AVIF is not an option here today. The AVIF button is added to the format row only when the browser reports that it can encode the format, and in our tests of September 2026 Chrome could not; use WebP. PNG has no quality setting, so it goes straight to the downscale stage and loses pixels until it fits; keep PNG for flat graphics and screenshots.
Check what your CMS serves, not only what you uploaded
A CMS may keep your upload and serve copies it made itself, at sizes and qualities of its own. This page cannot see that, but you can: open the published page, save the image it serves and drop it here. The input card prints its size, and after you generate, the result card prints its pixel dimensions. If they are not the ones on the card of the file you uploaded, the image was processed again after upload, and the CMS settings are where to look next.
The download also carries no EXIF: whatever the camera recorded, GPS coordinates included, is gone before a product shot taken at home lands on a public page.
Frequently asked questions
Is 300 KB too big for a blog post image?
For the hero or a full-width banner, no. For photos inside the post, our suggestion is a lower target: five 300 KB in-body images add 1.5 MB to the page. The Compress to 200 KB page runs the same search with that target.
A performance audit still flags the hero after it is under 300 KB. Why?
Because bytes are one check and pixels another. web.dev's guidance is to serve an image at the size it is displayed, and Chrome's Improve image delivery insight estimates savings by comparing the download size with an efficient bytes-to-pixel ratio for the format, ignoring anything under 4 KiB. A 1,600 px hero shown in a narrow phone column is oversized however little it weighs; smaller versions for small screens are what clears it.
Why did the output come back smaller in pixels than the original?
Because quality 50 did not get the file under 307,200 bytes at full size, so the page shrank it 15% per step until a quality of 50 or more fit; a PNG, which has no quality to search, takes that route too. To land on a width you chose instead, type it in Max width (px) and generate again.
Will the photo's GPS location end up on my site?
No. Every file this page writes has its EXIF stripped, GPS position included, and each card shows an EXIF stripped tag. The stripping happens in your browser along with the compression; nothing is sent anywhere.
Can I fix an image that is already published, or only new uploads?
Either. Start from the best original you still have rather than the copy the site serves, set its width, compress it here and upload the result in place of the old file. How the replacement is done depends on your CMS.
Can I run the hero and the in-post photos in one batch?
Yes, but every file in a run gets the same 307,200-byte target, and there is no per-file target on this page. Drop the hero and any full-width banners here, take the in-post photos to the 200 KB page in a second run, and download each batch as its own .zip.